Strange 4L80 Behavior

[Lightyear]

Yesterday after about 140 miles mostly on highway cruise at around 68mph/2400rpm, my Burb began acting funny. Leaving small town traffic it would not shift up into 4th, and no TC lock up. I checkde the ATF, level seems okay, no signs or odor of burnt fluid. All other gauges were normal. I had planned to service the tranny here shortly; anything I should be aware of at this point? This is my DD, so I want to get it solved fairly quick. Thanks, all!

[Robyn]

You need to get the thing on a scan tool (most tranny shops have one)
The real time data stream needs to be looked over to seem whats happening.

It could be as simple as a 3-4 shift solenoid gone south.

The scanner can tell if the ECM is calling for the shift and if the solenoid is energizing.

If the 3-4 solenoid does not activate the lockup will not happen either.

This test only takes a few minutes to do. Simply hook up the scanner, dial over to the trans fuctions and do a test drive.

If the Solenoid is the issue then its a fairly simple fix to remove the pan and replace the solenoid.

Once the pan is off you can the see if there are other issues such as excess crap in the pan (metal) and if all is well otherwise then a clean filter and fresh fluid is all thats needed.

If nothing else bad is found a complete fluid flush would be a good thing.

The shift solenoids do fail from time to time. This is not an ongoing or common thing but it does happen.

Without a scan its a guess as to whats wrong.

If the solemoid is activating then the issue is elsewhere.

There is also some O ring seals in the VB that can cause this issue too.


Keep us posted.

Missy

[Lightyear]

Thanks, Robyn. Will an Actron scan tool from my FLAPS do the business? That would be nice, so as to pick up all teh necessary bits at one stop. Otherwise I'll inquire at local tranny shops. Thanks again for the input.

[Robyn]

Not sure about the actron.


Robyn